Three potentially habitable planets the size of Earth discovered

PASADENA, Calif. -- Three potentially habitable planets roughly the size of Earth were discovered in a pair of distant star systems, NASA officials announced today, but it's still unknown if life could exist on any of them.

The planets were discovered by NASA's Kepler mission, which was developed by scientists at Jet Propulsion Laboratory in Pasadena.

"The Kepler spacecraft has certainly turned out to be a rock star of science," according to John Grunsfeld, associate administrator of the Science Mission Directorate at NASA Headquarters in Washington, D.C. "The discovery of these rocky planets in the habitable zone brings us a bit closer to finding a place like home.

"It is only a matter of time before we know if the galaxy is home to a multitude of planets like Earth, or if we are a rarity."

According to NASA, Kepler identified five planets orbiting a distant star, and two of them were orbiting at a distance that would make them suitable for liquid water. One is about 40 percent larger than Earth, making it the closest in size to Earth known to exist in the "habitable" zone of another star, according to the agency. The second planet is about 60 percent larger than Earth and is believed to be largely rocky.

The star system is about 1,200 light years from Earth.

The third potentially habitable planet, which was found orbiting a different star about 2,700 light years away, is about 70 percent larger than Earth. The planet orbits its star every 242 days, making it roughly equivalent to Venus, according to NASA.

"We only know of one star that hosts a planet with life -- the sun," according to Thomas Barclay, Kepler scientist at the Bay Area Environmental Research Institute in Sonoma. "Finding a planet in the habitable zone around a star like our sun is a significant milestone toward finding truly Earth-like planets."